Over the years, scientists have sought to grow animal cells in completely chemically defined culture media. However, for adequate growth, nearly all types of animal cells require not only a good chemically defined basal medium but, in addition, need a supplement of some naturally occuring biological fluid or tissue extract. These complex supplements have variously consisted of lymph, embryo extract, spinal fluid, skim milk, colostrum, blood plasma or blood serum. Because of its potency, availability and stability, bovine serum, particularly fetal bovine serum has become the most widely used supplement for cell culture. Fetal Bovine Serum known as FBS, is used as a supplement on a large scale in the areas of research, diagnostics, and the production of human and veterinary biologicals. In North America, several large corporations and many smaller companies, in association with the meat packing industry, collectively produce an estimated 150,000 liters of fetal bovine serum per annum. This quantity is produced from not less than about 300,000 liters of whole fetal blood. Thus, in the processing of whole blood to serum, on any scale whatever, the yield of serum is only 45% to 50% by volume of the original whole blood.
Bovine sera are generally produced from carefully drawn and collected whole blood from adult, calf, or fetal animals. Following the natural clotting processes, which may take several hours at 4.degree. C., the serum is separated and the residual clot is discarded, as described for example in U.S. Pat. No. 3,429,867. However, under less stringent bovine blood collection conditions, as when shed blood is taken at the time of slaughter, a quite different kind of clot is formed. In this situation, during exsanguination of the ox carcass, tissue juices from the slashed neck become admixed with the flowing blood and the mixture sets instantly to a rubbery, semi-solid, intractable mass. Such butchering clots are wasted at abattoirs but are an excellent source of growth-promoting materials according to the present invention. Therefore, in what follows, residual bovine blood clots from conventional serum processing as well as butchering bovine blood clots, inclusively, are the starting materials for the present invention.